Abstract: A structural element for forming a transition joint between a support bar and an associated mounting sleeve in the fabrication of support structure for holding prosthetic teeth. The element is precision molded of plastic and comprises a solid elongated body with an outwardly open elongated recess extending longitudinally of the body. The recess is sized to closely engage the associated mounting sleeve throughout the length of the recess. On the side of the body opposite the recess, there is an outwardly open elongated groove having a width to resiliently engage the support bar. In its preferred form, the groove and the recess have longitudinal axes which are in the same plane to assure that the support bar is in alignment with the axis of the support sleeve. Also, the recess has a generally semi-cylindrical configuration sized to conform to the exterior of the support sleeve and to make contact therewith throughout its length.